关于Unity中UGUI图片Image实现仿视频播放窗口的四角缩放功能

应用方法：将下面脚本挂载在需要实现四角缩放功能的UI图片上即可.

自定义拖拽精度（与边界距离多少内触发）m_validityWidth.

/*************************************************
 * 项目名称：UGUI通用
 * 脚本创建人：魔卡
 * 脚本创建时间：2017.12.14
 * 脚本功能：UI图片仿视频窗口缩放
 * ***********************************************/
using UnityEngine;
using System.Collections;
using System.Diagnostics;
using UnityEngine.EventSystems;
using Debug = UnityEngine.Debug;

//图片仿视频窗口缩放类
public class UIDragResizeByMocha : MonoBehaviour, IBeginDragHandler, IDragHandler, IEndDragHandler
{
    [Header( "有效检测的边缘宽度")]
    public float m_validityWidth = 10f;

    //存储操作的拖拽方向(默认为无操作)
    private DragDirection m_direction = DragDirection.None;

    //1.上方  //5.左上角
    //2.下方  //6.左下角
    //3.左方  //7.右上角
    //4.右方  //8.右下角

    //存储当前操作图片位置
    private Vector3 tTargetPos;
    //存储鼠标位置
    private Vector3 tMousePos;
    //存储当前图片宽度
    private float tWidth;
    //存储当前图片高度
    private float tHeight;

    //存储不动点位置坐标
    //解释一下：当我们拖动每个边界时至少有一个点时应该不动的，我们就以该点为基准点，当拖动单面有两点不动时我们取两点的中间点为基准点
    private Vector3 m_basePoint;

    /// <summary>
    /// 拖拽时刷新数据
    /// </summary>
    /// <param name="eventData"></param>
    void DoRefresh(PointerEventData eventData)
    {
        //刷新鼠标位置
        tMousePos = eventData.position;
        //刷新图片位置
        tTargetPos = transform.position;
        //刷新图片宽度
        tWidth = GetComponent<RectTransform>().sizeDelta.x;
        //刷新图片高度
        tHeight = GetComponent<RectTransform>().sizeDelta.y;
    }

    //拖动开始触发
    public void OnBeginDrag(PointerEventData eventData)
    {
        //刷新数据方法
        DoRefresh(eventData);
       
    }
    //拖动进行中触发
    public void OnDrag(PointerEventData eventData)
    {
        //刷新数据方法
        DoRefresh(eventData);

        #region 判定拖动方向
        //如果鼠标位置离左侧边界的限定距离内，设置对应的方向
        if (tMousePos.x < (tTargetPos.x - tWidth/2.0f + m_validityWidth))
        {
            m_direction = DragDirection.Left;
            //上
            if (tMousePos.y > (tTargetPos.y + tHeight/2.0f - m_validityWidth))
            {
                m_direction = DragDirection.LeftUp;
            }
                //下
            else if ((tMousePos.y < (tTargetPos.y - tHeight / 2.0f + m_validityWidth)))
            {
                m_direction = DragDirection.LeftDown;
            }
           
        }
        //如果鼠标位置离右侧边界的限定距离内
        else if(tMousePos.x > (tTargetPos.x + tWidth/2.0f - m_validityWidth))
        {
            m_direction = DragDirection.Right;
            //上
            if (tMousePos.y > (tTargetPos.y + tHeight / 2.0f - m_validityWidth))
            {
                m_direction = DragDirection.RightUp;
            }
            //下
            else if ((tMousePos.y < (tTargetPos.y - tHeight / 2.0f + m_validityWidth)))
            {
                m_direction = DragDirection.RightDown;
            }
        }
        //如果鼠标位置离上侧边界的限定距离内
        else if (tMousePos.y > (tTargetPos.y + tHeight / 2.0f - m_validityWidth))
        {
            m_direction = DragDirection.Up;
            //左
            if (tMousePos.x < (tTargetPos.x - tWidth/2.0f + m_validityWidth))
            {
                m_direction = DragDirection.LeftUp;
            }
            //右
            else if (tMousePos.x > (tTargetPos.x + tWidth/2.0f - m_validityWidth))
            {
                m_direction = DragDirection.RightUp;
            }
        }
        //如果鼠标位置离下侧边界的限定距离内
        else if ((tMousePos.y < (tTargetPos.y - tHeight/2.0f + m_validityWidth)))
        {
            m_direction = DragDirection.Down;
            //左
            if (tMousePos.x < (tTargetPos.x - tWidth/2.0f + m_validityWidth))
            {
                m_direction = DragDirection.LeftDown;
            }
            //右
            else if (tMousePos.x > (tTargetPos.x + tWidth/2.0f - m_validityWidth))
            {
                m_direction = DragDirection.RightDown;
            }
        }
        else
        {
            m_direction = DragDirection.None;
        }


    #endregion

        //根据当前判定的方向做出相应的仿视频窗口缩放
        switch (m_direction)
        {
            case DragDirection.Left :
                DoLeft();
                break;
            case DragDirection.Right :
                DoRight();
                break;
            case DragDirection.Up:
                DoUp();
                break;
            case DragDirection.Down :
                DoDown();
                break;
            case DragDirection.LeftUp :
                DoLeftUp();
                break;
            case DragDirection.LeftDown :
                DoLeftDown();
                break;
            case DragDirection.RightUp:
                DoRightUp();
                break;
            case DragDirection.RightDown :
                DoRightDown();
                break;
            default :
                Debug.Assert(false);
                break;
        }
            
    }

    #region 各个方向对应的调整方法
    /// <summary>
    /// 左拖动改变图片横向大小
    /// </summary>
    void DoLeft()
    {
        //设定基准点坐标
        m_basePoint = tTargetPos + new Vector3(tWidth/2.0f,0,0);
        //设定图片宽度
        float ttWidth = Mathf.Abs(m_basePoint.x - tMousePos.x);
        GetComponent<RectTransform>().sizeDelta = new Vector2(ttWidth, tHeight);
        //设置图片位置
        transform.position = m_basePoint - new Vector3(ttWidth/2.0f, 0, 0);
    }
    /// <summary>
    /// 右拖动改变图片横向大小
    /// </summary>
    void DoRight()
    {
        //设定基准点坐标
        m_basePoint = tTargetPos - new Vector3(tWidth / 2.0f, 0, 0);
        //设定图片宽度
        float ttWidth = Mathf.Abs(m_basePoint.x - tMousePos.x);
        GetComponent<RectTransform>().sizeDelta = new Vector2(ttWidth, tHeight);
        //设置图片位置
        transform.position = m_basePoint + new Vector3(ttWidth / 2.0f, 0, 0);
    }
    /// <summary>
    /// 上拖动改变图片横向大小
    /// </summary>
    void DoUp()
    {
        //设定基准点坐标
        m_basePoint = tTargetPos - new Vector3(0, tHeight /2.0f, 0);
        //设定图片高度
        float ttHeight = Mathf.Abs(m_basePoint.y - tMousePos.y);
        GetComponent<RectTransform>().sizeDelta = new Vector2(tWidth, ttHeight);
        //设置图片位置
        transform.position = m_basePoint + new Vector3(0, ttHeight/2.0f, 0);
    }
    /// <summary>
    /// 下拖动改变图片横向大小
    /// </summary>
    void DoDown()
    {
        //设定基准点坐标
        m_basePoint = tTargetPos + new Vector3(0, tHeight / 2.0f, 0);
        //设定图片高度
        float ttHeight = Mathf.Abs(m_basePoint.y - tMousePos.y);
        GetComponent<RectTransform>().sizeDelta = new Vector2(tWidth, ttHeight);
        //设置图片位置
        transform.position = m_basePoint - new Vector3(0, ttHeight / 2.0f, 0);
    }
    /// <summary>
    /// 左上拖动改变图片横向大小
    /// </summary>
    void DoLeftUp()
    {
        //设定基准点坐标
        m_basePoint = tTargetPos + new Vector3(tWidth / 2.0f, -tHeight /2.0f, 0);
        //设定图片宽度
        float ttWidth = Mathf.Abs(m_basePoint.x - tMousePos.x);
        //设定图片高度
        float ttHeight = Mathf.Abs(m_basePoint.y - tMousePos.y);
        GetComponent<RectTransform>().sizeDelta = new Vector2(ttWidth, ttHeight);
        //设置图片位置
        transform.position = m_basePoint + new Vector3(-ttWidth / 2.0f, ttHeight / 2.0f, 0);
    }
    /// <summary>
    /// 左下拖动改变图片横向大小
    /// </summary>
    void DoLeftDown()
    {
        //设定基准点坐标
        m_basePoint = tTargetPos + new Vector3(tWidth / 2.0f, tHeight / 2.0f, 0);
        //设定图片宽度
        float ttWidth = Mathf.Abs(m_basePoint.x - tMousePos.x);
        //设定图片高度
        float ttHeight = Mathf.Abs(m_basePoint.y - tMousePos.y);
        GetComponent<RectTransform>().sizeDelta = new Vector2(ttWidth, ttHeight);
        //设置图片位置
        transform.position = m_basePoint + new Vector3(-ttWidth / 2.0f, -ttHeight / 2.0f, 0);
    }
    /// <summary>
    /// 右上拖动改变图片横向大小
    /// </summary>
    void DoRightUp()
    {
        //设定基准点坐标
        m_basePoint = tTargetPos + new Vector3(-tWidth / 2.0f, -tHeight / 2.0f, 0);
        //设定图片宽度
        float ttWidth = Mathf.Abs(m_basePoint.x - tMousePos.x);
        //设定图片高度
        float ttHeight = Mathf.Abs(m_basePoint.y - tMousePos.y);
        GetComponent<RectTransform>().sizeDelta = new Vector2(ttWidth, ttHeight);
        //设置图片位置
        transform.position = m_basePoint + new Vector3(ttWidth / 2.0f, ttHeight / 2.0f, 0);
    }
    /// <summary>
    /// 右下拖动改变图片横向大小
    /// </summary>
    void DoRightDown()
    {
        //设定基准点坐标
        m_basePoint = tTargetPos + new Vector3(-tWidth / 2.0f, tHeight / 2.0f, 0);
        //设定图片宽度
        float ttWidth = Mathf.Abs(m_basePoint.x - tMousePos.x);
        //设定图片高度
        float ttHeight = Mathf.Abs(m_basePoint.y - tMousePos.y);
        GetComponent<RectTransform>().sizeDelta = new Vector2(ttWidth, ttHeight);
        //设置图片位置
        transform.position = m_basePoint + new Vector3(ttWidth / 2.0f, -ttHeight / 2.0f, 0);
    }
    #endregion 
    
    //拖动结束触发
    public void OnEndDrag(PointerEventData eventData)
    {
        //重置拖动方向
        m_direction = DragDirection.None;
    }

}

/// <summary>
/// 拖拽方向枚举
/// </summary>
public enum DragDirection
{
    None,       //无
    Up,         //上
    Down,       //下
    Left,       //左
    Right,      //右
    LeftUp,     //左上
    RightUp,    //右上
    LeftDown,   //左下
    RightDown   //右下
}